DE10039773A1 - Fuel supply system - Google Patents

Abstract

In the case of fuel supply systems with two pumps connected in series and fuel valves injecting directly into the combustion chamber, there have previously been problems at higher temperatures due to insufficient delivery of the second fuel pump. DOLLAR A It is now proposed to provide a shut-off valve (30), which is closed at a higher temperature, and a flushing line (60), through which fuel is passed to the fuel reservoir (2) at a higher temperature. This is intended to dissipate as much thermal energy as possible from the second fuel pump (12) and to counteract the formation of gas bubbles by means of a higher feed pressure. DOLLAR A The device is intended for an internal combustion engine of a vehicle.

Description

State of the art

The invention relates to a fuel supply system for supplying fuel for an internal combustion engine according to the preamble of claim 1.

So far there have been fuel supply systems where one first fuel pump from a fuel tank Fuel through a fuel connection to a second one Fuel pump delivers. Your second fuel pump on the other hand, the fuel feeds via a pressure line at least one fuel valve. Usually that is Number of fuel valves equal to the number of cylinders the internal combustion engine. The fuel supply system can be built so that the fuel valve runs on the fuel injected directly into a combustion chamber of the internal combustion engine. When operating this fuel supply system is a high pressure in the pressure leading to the fuel valve line required. For security reasons and never completely excluded leakage of the fuel valve in the combustion chamber it is useful after turning off the Internal combustion engine the pressure in the fuel connection and in the pressure line of the fuel supply system entirely or at least largely dismantle it.  

The German patent application DE 195 39 885 A1 shows one Fuel supply system at which to start the burning engine a valve device ensures that the first fuel pump during the starting process Fuel with increased feed pressure to the fuel valves supplies. In many cases this is sufficient Feed pressure out to the internal combustion engine in no time to start. Due to the increased feed pressure, a possible gas bubble in the fuel connection between the first fuel pump and the second fuel pump in many cases are compressed so far that a more secure Operation of the internal combustion engine is guaranteed. Nevertheless it can be particularly high at temperatures during the Operation of the internal combustion engine and especially when the engine is turned off at high temperature problems with startup and also Problems operating the internal combustion engine during high temperatures come. As has now been established this is obviously because the gas bubble though largely compressed by the increased feed pressure, however not sufficient from the fuel supply system is removed. Furthermore, it has now been found that through insufficient heat dissipation from the fuel supply care system there are problems with high operating temperature of the Internal combustion engine can give.

Advantages of the invention

The fuel supply system according to the invention with the characterizing features of claim 1 offers the front partial possibility with particularly high heat load the fuel in the fuel supply system, ins special but also with particularly high heat loads especially the second fuel pump to ensure that adequate heat dissipation from the lines of the  Fuel supply system is made and that no gas bubbles arise within the lines. Especially because of the Flushing line can put fuel in the fuel tank be returned, which is a beneficial heat dissipation allows. Due to the closable shut-off valve the removal of the fuel via the flush line increased pressure in the fuel connection between the two fuel pumps so that an effective flushing is guaranteed and that it is also guaranteed that on Entrance to the second fuel pump no gas bubbles or Vapor bubbles occur. This will be advantageous reliably a drop in performance especially of the second Fuel pump reliable even at high temperatures prevented and even at high temperature is a verver guaranteed smooth starting of the engine.

By the dimension listed in the dependent claims are advantageous further training and improvements the fuel supply system according to claim 1 possible.

drawing

Selected, particularly advantageous exemplary embodiments of the invention are shown in simplified form in the drawing and are explained in more detail in the following description. 1, there is shown in FIGS., A first embodiment, Fig. 2 shows a second embodiment, FIG. 3 alignment, for example a third stop, the Fig. 4 shows a detail, Fig. 5 shows a fourth embodiment, FIG. 6 shows a fifth embodiment, FIGS. 7 for a sixth execution, Fig. 8, a seventh embodiment, FIG. 9, an eighth embodiment, FIG. 10 is a detail view corresponding to FIG. 11, a ninth embodiment and Fig. 12, a tenth embodiment.

Description of the embodiments

The fuel supply system according to the invention Metering of fuel for an internal combustion engine can different types of internal combustion engines are used become. The same applies to the invention Method for operating an internal combustion engine. The focal The engine is, for example, a gasoline engine with an external one or internal mixture formation and spark ignition, whereby the. Engine with a reciprocating piston (reciprocating piston engine) or with a rotatably mounted piston (Wankel piston Motor) can be provided. The internal combustion engine can for example, a hybrid engine. With this engine with charge stratification, the fuel-air mixture in the Enriched the area of the spark plug so that a safe ignition is guaranteed, the combustion in the Medium but takes place when the mixture is very emaciated.

The gas change in the combustion chamber of the internal combustion engine can for example, according to the four-stroke process or Two-stroke procedures take place. To control the gas change in The combustion chamber of the internal combustion engine can be in a known manner Gas exchange valves (intake valves and exhaust valves) featured to be seen. The internal combustion engine can be designed that at least one fuel valve direct the fuel injected into the combustion chamber of the internal combustion engine. The Control of the performance of the internal combustion engine is carried out preferably by controlling the supply to the combustion chamber Amount of fuel. But it can also be provided that the fuel valve the fuel at the inlet valve Combustion chamber upstream. In this version, the for the Combustion of the fuel air supplied to the combustion chamber usually controlled with a throttle valve. About the Position of the throttle valve can depend on the internal combustion engine machine output to be controlled.  

The internal combustion engine has a cylinder, for example with a piston, or it can be with multiple cylinders and be provided with a corresponding number of pistons. A fuel valve is preferably provided for each cylinder see.

To the extent of the description not unnecessarily extensive to drop out, the following is limited Description of the exemplary embodiments on a reciprocating piston engine with four cylinders as an internal combustion engine, the four fuel valves the fuel, usually gasoline, directly into the combustion chamber of the internal combustion engine squirt. The performance of the internal combustion engine is about Controlled the amount of fuel injected. at At idle and (lower) partial load there is a charge stratification with fuel enrichment in the area of the ignition candle. Outside of this range, the mixture is very lean. At full load or upper part load, a homogeneous Ver division between fuel and air in the combustion chamber sought.

Fig. 1 shows a fuel tank 2, a suction line 4, a first fuel pump 6, a pressure relief valve 7, an electric motor 8, a fuel connection 10, a second fuel pump 12, a pressure line 14, the four fuel valves 16, and a controller 20. The fuel valves 16 are often referred to in the art as injection valves or injectors.

The first fuel pump 6 has a pressure side 6 h and a suction side 6 n. The second fuel pump 12 has a high pressure side 12 h and a low pressure side 12 n. The fuel connection 10 leads from the pressure side 6 h of the first fuel pump 6 to the low pressure side 12 n of the second Fuel pump 12 . From the pressure side 6 h of the first fuel pump 6 , a channel leads back into the fuel reservoir 2 . The pressure relief valve 7 is provided in this channel.

A fuel line 22 branches off from the fuel connection 10 . Via the fuel line 22 , fuel can be returned from the fuel connection 10 into the fuel tank 2 . In the course of the fuel connection 10 , between the first fuel pump 6 and the second fuel pump 12 , there is a filter 24 .

A pressure control valve 26 and a shut-off valve 30 are provided in the fuel line 22 . The pressure control valve 26 and the shut-off valve 30 are operatively connected in series. That is, the pressure control valve 26 and the shut-off valve 30 are connected in series in terms of circuitry. The pressure control valve 26 and the valve device 30 can also be implemented in a compact manner in a common housing.

The shut-off valve 30 has a first switching position 30 a and a second switching position 30 b. In the first switching position 30 a, fuel can flow from the fuel connection 10 through the fuel line 22 via the pressure control valve 26 into the fuel reservoir 2 . In this switching position, the pressure control valve 26 directly determines the feed pressure of the fuel in the fuel connection 10 . The shut-off valve 30 is in its second switching position 30 b, then the fuel cannot flow directly from the fuel connection 10 to the pressure control valve 26 .

The first fuel pump 6 is driven by the electric motor 8 . The first fuel pump 6 , the pressure relief valve 7 , the electric motor 8 , the filter 24 , the pressure control valve 26 and the shut-off valve 30 are located in the area of the fuel reservoir 2 . These parts are preferably arranged on the outside of the fuel tank 2 or are located inside the fuel tank 2 .

The second fuel pump 12 is mechanically coupled to an output shaft of an internal combustion engine 32 shown symbolically via mechanical transmission means 12 m. The camshaft of the internal combustion engine 32 serves as an output shaft. Since the second fuel pump 12 is mechanically coupled to the output shaft of the internal combustion engine 32 , the second fuel pump 12 operates in proportion to the speed of the output shaft of the internal combustion engine 32 . Because the second fuel pump 12 is spatially flanged to the housing of the internal combustion engine 32 , a strong heating of the internal combustion engine 32 is transferred to the second fuel pump 12 , which causes a relatively high thermal load on the fuel in the fuel supply system.

The pressure line 14 leading from the second fuel pump 12 to the fuel valves 16 can be simply divided into a line section 42 , a storage space 44 and a plurality of distribution lines 46 . The fuel valves 16 are each connected to the storage space 44 via a distribution line 46 . A pressure sensor 48 is connected to the storage space 44 and senses the respective pressure of the fuel in the pressure line 14 . According to this pressure, the pressure sensor 48 sends an electrical signal to the control device 20 .

A control valve 50 which is electrically controllable by the control device 20 is connected to the storage space 44 of the pressure line 14 . Depending on the control of the control valve 50 , fuel is passed from the pressure line 14 via a circulation line 52 to the low pressure side 12 n of the second fuel pump 12 . Between the control valve 50 and the low pressure side 12 n, a hydraulic resistance element is arranged. The resistance element is a return check valve 53 , which opens in the direction of the fuel connection 10 even at a very low pressure difference.

The first fuel pump 6 is, for example, a pump driven by the electric motor 8, which conveys a certain amount of fuel per revolution due to its design. The pressure of the fuel on the pressure side 6 h of the first fuel pump 6 is referred to below as the feed pressure. When the shut-off valve 30 is open, the pressure control valve 26 determines the level of the feed pressure in the fuel connection 10 . The pressure control valve 26 is, for example, a differential pressure of 3 bar. So the feed pressure in the fuel connection 10 when the shut-off valve 30 is open is three bar (3 bar).

A flush line 60 leads from the second fuel pump 12 into the fuel reservoir 2 . Within the pump housing 12 g, the flush line 60 is connected to the low pressure side 12 n of the fuel pump 12 , as can be seen in FIG. 4. There is hydraulic resistance in the course of the flush line 60 . The hydraulic resistance is formed by a first overflow valve 61 and a second overflow valve 62 . There is a branch 63 in the course of the circulation line 52 . The flushing line 60 branches off from the circulation line 52 at the branch 63 . In the particularly advantageous and therefore preferably selected exemplary embodiment shown in FIG. 1, the flushing line 60 opens at an opening 64 between the shut-off valve 30 and the pressure control valve 26 into the fuel line 22 . The first overflow valve 61 is set to a relatively low differential pressure, preferably to 1 bar. The second overflow valve 62 is set to a relatively low differential pressure, preferably to 1 bar. Because the set differential pressure at the two overflow valves 61 , 62 can each be chosen to be quite low, the overflow valves 61 , 62 can advantageously be chosen to be of a construction which is fairly simple to manufacture, without this resulting in strong scattering in the set differential pressure.

The first fuel pump 6 normally promotes a bit more fuel into the fuel connection 10 and is removed from the second fuel pump 12 from the fuel connection 10 degrees. In the normal operating state, the excess fuel flows through the normally open shut-off valve 30 and through the pressure control valve 26 , so that in the fuel connection 10 the pressure resulting from the differential pressure at the pressure control valve 26 results.

If a sensor 65 detects that the temperature is particularly high, a corresponding signal is delivered to the control device 20 . The control device 20 then switches the shut-off valve 30 in the second switching position 30 b, in which the direct connection from the fuel connection 10 to the pressure control valve 26 is interrupted. When the shut-off valve 30 is closed, the excess fuel not removed from the second fuel pump 12 from the fuel connection 10 flows through the pump housing 12 g of the second fuel pump 12 , through the first overflow valve 61 , through the second overflow valve 62 and through the pressure control valve 26 back into the Fuel tank 2 . This results in a closed shut-off valve 30 in the fuel connection 10, a feed pressure which corresponds to the sum of the differential pressures of the valves 61 , 62 and 26 . In the selected exemplary embodiment, the pressure relief valve 7 is set, for example, to a pressure which is higher than the sum of the differential pressures of the valves 61 , 62 and 26 .

Because the purge line 60 leads through the pump housing 12 g of the second fuel pump 12 , thermal energy can be dissipated from the second fuel pump 12 through the fuel flowing through the purge line 60 , as a result of which the temperature of the fuel in the area of the fuel connection 10 and in the area of the fuel is too high second fuel pump 12 is avoided. The fact that the feed pressure in the fuel connection 10 when the shut-off valve 30 is closed is higher than the feed pressure in the normal operating state of the internal combustion engine 32 , ensures that even an unusually high temperature does not lead to gas bubbles in the fuel connection 10 , which means that even under high thermal loads, none Deterioration in the efficiency of the fuel pump 12 must be feared. Because the increased feed pressure is only set at a fairly high temperature, that is, usually only for a relatively short time, this does not result in a noticeable reduction in the durability of the first fuel pump 6, which can be produced relatively cheaply.

Because the excess fuel delivered by the second fuel pump 12 in the pressure line 14 , which is not removed by the fuel valves 16 , and which is controlled by the control valve 50 from the storage space 44 , via the circulation line 52 through the check valve 53 directly to the low pressure side 12 n of the second fuel pump 12 is guided, unnecessary paths for the circuit of the fuel are avoided and in the normal operating state of the internal combustion engine no heated fuel is led into the fuel reservoir 2 from the area of the pressure line 14, which results in the normal operating temperature of the internal combustion engine 32 unnecessary heating of the fuel in the fuel tank 2 is avoided.

The fuel pump 12 has a pump housing 12 g indicated by dashed lines in the drawing. The overflow valves 61 , 62 , the check valve 53 , the branch 63 and the sensor 65 are preferably provided within the pump housing 12 g.

The sensor 65 is, for example, a temperature sensor and it can be arranged, for example, directly in the pump housing 12 g or in the area of the pressure line 14 . To measure the temperature, the water temperature of the cooling water of the internal combustion engine 32 can also be used instead of the sensor 65, for example.

Fig. 2 shows a further preferably selected, especially advantageous exemplary embodiment.

The same or equivalent parts are included in all the figures provided the same reference numerals. Unless nothing against it Part mentioned or in the drawing Darge is, that applies to one of the figures and Shown also in the other embodiments. Unless otherwise stated in the explanations, are the details of the various embodiments can be combined with each other.

In contrast to FIG. 1, the flushing line 60 in the exemplary embodiment shown in FIG. 2 is guided downstream of the second overflow valve 62 directly into the fuel reservoir 2 . In order to obtain an equally high feed pressure when the shut-off valve 30 is closed, as explained with reference to FIG. 1, the differential pressure of the second overflow valve 62 is not set to, for example, 1 bar as in the first exemplary embodiment, but, for example, to 5 bar.

In the embodiment shown in FIGS . 1 and 2, an intermediate piece of the flushing line 60 between the first overflow valve 61 and the second overflow valve 62 is merged with an intermediate piece of the circulation line 52 between the control valve 50 and the check valve 53rd This results in an effective flushing of both the fuel connection 10 and the housing 12 g of the second fuel pump 12 and also a flushing and thus heat dissipation from the circulation line 52 .

Fig. 3 shows a further, preferred selected, especially advantageous exemplary embodiment.

In the embodiment shown in FIG. 3, the fuel passes from the low pressure side 12 n of the fuel pump 12 , via an overflow valve 66 , through the flush line 60 and via the pressure control valve 26 into the fuel reservoir 2 . The overflow valve 66 forms a hydraulic resistance in the flush line 60 .

In contrast to the exemplary embodiments shown in FIGS . 1 and 2, the flushing line 60 downstream of the overflow valve 66 is not brought together with the circulating line 52 in FIG. 3. This gives the advantage that fewer valves are required. Nevertheless, in the embodiment shown in FIG. 3, for example, at least one indirect venting of the circulation line 52 via the check valve 53 , the low pressure side 12 n of the fuel pump 12 and the flush line 60 with the overflow valve 66 is possible.

In order to obtain the same pressure ratios in the exemplary embodiment shown in FIG. 3 as in the exemplary embodiments explained with reference to FIGS. 1 and 2, the differential pressure of the overflow valve 66 is set to 2 bar in FIG. 3, for example.

In the execution examples shown in FIGS. 1 to 3, the pressure relief valve 7 can in principle be dispensed with. However, it is proposed to provide the pressure relief valve 7 as protection in the event of a clogged filter 24 even in these exemplary embodiments.

FIG. 4 shows a longitudinal section through the second fuel pump 12.

The fuel pump 12 has at least one pump piston 12 p. The fuel pump 12 preferably has three pump pistons 12 p, of which only one is shown for the sake of clarity. The fuel reaches the interior of the pump housing 12 g via the fuel connection 10 . The low pressure side 12 n and the at least one pump piston 12 p are located in the pump housing 12 g. The pump piston 12 p is surrounded by the fuel, the fuel has the same feed pressure as in the fuel connection 10th The flushing line 60 branches off at the highest point of the interior of the housing 12 g of the fuel pump 12 . It is thereby achieved that the air collecting at the highest point in the pump housing 12 g is discharged through the flushing line 60 to the fuel tank 2 .

FIG. 5 shows a further preferably selected, especially advantageous exemplary embodiment.

Immediately downstream of the first fuel pump 6 , the channel leading into the fuel reservoir 2 branches off on the pressure side 6 h of the fuel pump 6 . The pressure relief valve 7 is located within the channel. The pressure relief valve 7 is set to 8 bar, for example. The pressure relief valve 7 is, in the flow direction be, still before the filter 24 to ensure that a blockage at any point does not lead to an excessive pressure in the fuel pump 6 .

The branch 63 is located between the control valve 50 and the check valve 53 , at which the flushing line 60 branches off from the circulation line 52 . In the course of the flush line 60 , a hydraulic resistance is provided. The hydraulic resistance is formed by a throttle 70 .

The check valve 53 has a biasing spring. The pre-clamping pressure of the check valve 53 is matched to the flow resistance of the throttle 70 , in such a way that even when the shut-off valve 30 is in its open switching position 30 a, from the circulation line 52 a desired amount of fuel via the flush line is constantly present 60 and flows through the pressure control valve 26 to the fuel tank 2 .

If the shut-off valve 30 is in its closed switching position 30 b, then the excess fuel delivered by the first fuel pump 6 , but not removed from the fuel valves 16, flows through the pressure relief valve 7 into the fuel reservoir 2 , and part of the excess fuel delivered flows through the throttle 70 and through the pressure control valve 26 to the fuel tank 2 . Because the pressure at the pressure relief valve 7 is set higher than the differential pressure at the pressure control valve 26 and because the fuel flowing through the flushing line 60 is also accumulated at the throttle 70 , a feed pressure results in the fuel connection 10 when the shut-off valve 30 is closed, which pressure is significantly higher than the feed pressure occurring in the normal operating state with the shut-off valve 30 open. This achieves reliable compression of any gas bubbles that may occur in the fuel connection 10 or in the fuel pump 12 , and a flushing of part of the fuel from the circulation line 52 back to the fuel reservoir 2 is achieved . As a result, an additional removal of undesirable thermal energy occurring in the fuel supply system is achieved. By adjusting the biasing pressure of the check valve 53 via the spring, the portion of the fuel that flows directly from the circulation line 52 to the low pressure side 12 n of the fuel pump 12 and the portion of the fuel flowing through the flushing line 60 back to the fuel reservoir 2 can be coordinated ,

In the exemplary embodiment shown in FIG. 5, the throttle 70 ensures that a certain proportion of the fuel, which proportion can be selected by appropriately set preload for the check valve 53 , is continuously returned from the circulation line 52 into the fuel storage container 2 even in normal operation becomes.

Fig. 6 shows a further preferably selected, especially advantageous exemplary embodiment.

Deviating from FIG. 5, in the Fig. 6 embodiment shown, the hydraulic resistance in the irrigation line is formed in which 60 of a provided in the purge line 60 overflow valve 72nd The overflow valve 72 is set, for example, so that it opens when a differential pressure of 2 bar is present. The check valve 53 is set such that it opens, for example, even at a very low differential pressure. This ensures that in the normal operating state of the fuel supply system, that is, when the shut-off valve 30 is in its open switch position 30 a, the feed pressure in the fuel connection 10 is determined by the pressure control valve 26 , and the one promoted by the second fuel pump 12 and not by Fuel removed from the fuel valves 16 flows in a short way from the high pressure side 12 h via the control valve 50 , through the circulation line 52 and via the check valve 53 to the low pressure side 12 n of the fuel pump 12 . The biased overflow valve 72 ensures that no fuel flows back from the circulation line 52 to the fuel reservoir 2 . This ensures that the temperature of the fuel in the fuel tank 2 is kept as low as possible in the normal operating state of the fuel supply system.

In order to achieve flushing, the shut-off valve 30 is switched to the closed switching position 30 b. As a result, the feed pressure in the fuel connection 10 rises to a maximum of the pressure set at the pressure relief valve 7 , and due to this increased feed pressure, the biasing pressure of the overflow valve 72 is exceeded and fuel flows from the circulation line 52 , via the overflow valve 72 and via the pressure control valve 26 into the Fuel tank 2 .

Fig. 7 shows a further preferably selected, especially advantageous exemplary embodiment.

In a departure from the embodiment shown in FIG. 6, the exemplary embodiment shown symbolically in FIG. 7 has a further hydraulic resistance element in the course of the circulation line 52 . The further resistance element is a choke 74 . The throttle 74 is hydraulically in series with the check valve 53 . When viewed in the direction of flow, the throttle 74 can be located before or after the check valve 53 . The throttle 74 and the check valve 53 are located downstream downstream of the branch 63 to the flushing line 60 .

With the throttle 74 it is achieved that, when a relatively large amount of fuel is pumped in the circulation line 52 at a higher speed of the internal combustion engine 32 , a back pressure arises in front of the throttle 74 and if this back pressure is large enough to the prestressed overflow valve 72 overcome, at least a portion of the fuel pumped by the second fuel pump 12 flows back into the fuel tank 2 .

The embodiment shown in FIG. 7 can be coordinated so that at a higher speed of the internal combustion engine 32 , part of the fuel flows back from the circulation line 52 into the fuel tank 2 without having to switch the shut-off valve 30 into its closed switching position 30 b in an increased feed pressure must be set in the fuel connection 10 . This has the advantage that at an increased speed of the internal combustion engine 32 , which can occur frequently depending on the driving style, the first fuel pump 6 does not have to work against an increased feed pressure, which significantly increases its durability. In the exemplary embodiment according to FIG. 7, the shut-off valve 30 has to be switched only briefly, for example only for flushing the fuel lines during the starting process of the internal combustion engine 32 , into the closed switching position 30 b, which means that the fuel pump 6 is only correspondingly seldom against an increased one Feed pressure must work, which significantly extends the durability of the fuel pump 6 .

Fig. 8 shows a further preferably selected, especially advantageous exemplary embodiment.

In the example shown in the Fig. 8 embodiment are the throttle 74 and the check valve 53 in the course of the circulation line 52 hydraulically seen after the branch 63, to which the purge line 60 from the line 52 branching circulation. Regarded hydraulically, the throttle 74 and the check valve 53 are located parallel to one another. The check valve 53 is biased with a closing spring. The check valve 53 only opens when, due to a relatively high pressure medium flow at the throttle 74, there is a sufficient differential pressure to open the check valve 53 . The check valve 53 thus limits the pressure drop across the throttle 74 .

From an hydraulic point of view downstream of the branch 63 , an additional hydraulic resistance is provided in the flushing line 60 . The additional hydraulic resistance was formed by a throttle 76 . The throttle 76 is considered hydraulically in series with the overflow valve 72 before or after the spill valve 72nd

By tuning the throttles 74 and 76 and the bias pressures of the check valve 53 and the overflow valve 72 , the fuel flow flowing through the flushing line 60 to the fuel reservoir 2 and the fuel flow 12 flowing through the circulation line 52 to the low pressure side 12 n of the fuel pump can be coordinated with one another. It can also be determined from which speed of the internal combustion engine 32 a part of the fuel flow flowing through the circulation line 52 flows back via the flush line 60 to the fuel tank 2 .

Fig. 9 shows a further preferably selected, especially advantageous exemplary embodiment.

FIG. 10 shows a detailed view of the exemplary embodiments illustrated in FIGS. 9, 11 and 12.

In the embodiment shown in FIGS. 9 and 10, the second fuel pump 12 has a pump piston 12 p, an input-side check valve 12 a, an output-side check valve 12 b, a compression chamber 12 k and a control valve 50 '.

A pressure damper 78 is connected to the fuel connection 10 . The pressure damper 78 is preferably within the pump housing 12 g. In the course of the circulation line 52 'there is a hydraulic resistance element. The resistance element is a check valve 80 , which opens in the direction of the fuel connection 10 . At an opening 82 , the circulation line 52 'opens into the fuel compound 10th The circulation line 52 ′ leads from the compression space 12 k, through the control valve 50 ′, via the branch 63 ′, through the check valve 80 and via the junction 82 into the fuel connection 10 . The circulation line 52 'runs a short distance directly within the pump housing 12 g. The control valve 50 'has an open switching position 50' a and a closed switch position 50 b '. At the branch 63 'provided between the control valve 50 ' and the check valve 80 , the flushing line 60 branches off. Downstream behind the branch 63 ', the purge line 60 has a hydraulic resistance. The hydraulic resistance is formed by a throttle 84 .

A line 86 leads from the fuel connection 10 into the region of the piston guide of the piston 12 p. The feed pressure supplied via line 86 to the piston guide ensures a reduction in friction in the area of the piston guide.

From the area of the compression space 12 k end of the pump piston 12 facing away p performs a leakage line 88 in the fuel line 22nd Downstream behind the pressure control valve 26, there is a second shut-off valve 90 in the fuel line 22 . The second shut-off valve 90 has an open switching position 90 a and a closed switching position 90 b. The leakage line 88 opens between the pressure control valve 26 and the second shut-off valve 90 at an opening 92 in the fuel line 22 .

During a suction stroke, that is, while the pump piston 12 p moves downward and thereby increases the compression space 12 k, the fuel flows from the fuel connection 10 through the check valve 12 a on the input side into the compression space 12 k. During a pressure stroke, that is, while the pump piston 12 p moves upward and thereby compresses the compression space 12 k, the pump piston 12 p presses the fuel from the compression space 12 k via the check valve 12 b on the outlet side into the storage space 44 of the pressure line 14 , if the control valve 50 'is in its closed switching position 50 ' b. It is possible, the control valve 50 'to be driven so that it is in the open switch position p 50 during part of the compression stroke of the pump piston 12' is a. While the control valve 50 'position during the pressure stroke in the open switch 50' a is, the fuel is due to the normally high pressure in the pressure line 14 via the open control valve 50 'by the circulation line 52' and via the check valve 80 in the fuel connection 10 promoted. The throttle 84 and the prestressed check valve 80 can be coordinated with one another such that when the control valve 50 'is open during the pressure stroke, part of the fuel flowing through the circulation line 52 ' through the flush line 60 and via the pressure control valve 26 into the fuel reservoir 2 flows back.

By appropriate, depending on the stroke of the pump piston 12 p from switching the control valve 50 'in the switching positions 50 ' a or 50 'b, the amount of fuel delivered by the second fuel pump 12 into the pressure line 14 can be controlled. By correspondingly controlling the control valve 50 ′, the quantity delivered by the fuel pump 12 into the pressure line 14 can be controlled in such a way that the desired high pressure prevails in the pressure line 14 , which can be sensed by the pressure sensor 48 . Depending on the pressure determined by the pressure sensor 48 , the control valve 50 'is activated.

A return line 94 leads from the pressure line 14 to the storage space 44 into the fuel connection 10 . In the return line 94 there is a pressure relief valve 96 . The pressure limiting valve 96 is provided so that no dangerous overpressure can arise in the pressure line 14 even if an error occurs, for example when the control valve 50 'is working incorrectly. The pressure relief valve 96 can also be electrically controllable, in such a way that, depending on the operating condition, the pressure in the storage space 44 can be quickly reduced.

If the shut-off valve 30 is in its open switching position 30 a, then, depending on how the throttle 84 and the pressure difference of the check valve 80 are coordinated with one another, for example only a very small part of the fuel flow flowing through the circulation line 52 ′ flows through the flushing line 60 into the fuel tank 2 . The usually larger fuel flow flows through the check valve 80 into the fuel connection 10 , where the pressure damper 78 is provided in order to temporarily store the fuel to be pulsed.

If the shut-off valve 30 is in its closed switching position 30 b, then the pressure relief valve 7 determines the feed pressure in the fuel connection 10 . Is because the pressure relief valve 7 to a higher pressure than the set pressure control valve 26, the supply pressure at ge schlossenem shut-off valve 30 is higher than in the open shut-off valve from 30th When the switch position 30 b of the shut-off valve 30 is closed , the fuel flow flowing from the compression space 12 k through the control valve 50 ′ essentially flows through the throttle 84 , through the flushing line 60 into the fuel line 22 and from there into the fuel reservoir 2 .

While the engine 32 is operating, the second shut-off valve 90 is usually in its open switching position 90 a. If the engine 32 is turned off, then the second shut-off valve 90 is switched to its closed switching position 90 b, thereby avoiding premature pressure reduction in the low-pressure system via the gap between the pump piston 12 p and the pump housing 12 g.

Fig. 11 shows a further preferably selected, especially advantageous exemplary embodiment.

In contrast to the exemplary embodiment shown in FIG. 9, the leakage line 88 is guided in the exemplary embodiment shown in FIG. 11 without using the fuel line 22 in the fuel tank 2 . The shut-off valve 90 is provided in the course of the leakage line 88 . Because only a very small amount of fuel flows through the leakage line 88 , which is many times smaller than the amount of fuel flowing through the fuel line 22 , a very small and very easy to produce valve is sufficient for the shut-off valve 90 .

Fig. 12 shows a further preferably selected, especially advantageous exemplary embodiment.

In the exemplary embodiment shown in FIG. 12, the shut-off valve 30 is arranged downstream of the pressure control valve 26 in the fuel line 22 , viewed in the flow direction. The purge line 60 branches off from the fuel connection 10 at a branch 63 ″. Downstream behind the throttle 84 , the leakage line 88 opens into the flushing line 60 . The junction 64 , at which the flush line 60 opens into the fuel line 22 , is provided between the pressure control valve 26 and the shut-off valve 30 .

The control valve 50 'is connected to the fuel connection 10 via the circulation line 52 ' and via the junction 82 . During the suction stroke of the fuel pump 10, the force can material with open control valve 50 'not only by the input-side check valve 12 a, but additionally also through the control valve 50' to flow into the compression chamber 12 k. During the pressure stroke of the fuel pump 12 , the control valve 50 'is held in the closed switching position 50 ' b until the pressure desired in the pressure line 14 is reached.

In Fig. 12 two dash-dotted lines 98 r and 98 f are drawn. Usually, the components shown on the left of the dash-dotted line 98 r are in the rear area of the motor vehicle, and the components on the right of the dash-dotted line 98 f are usually in the front area of the motor vehicle.

Usually, in order to connect the components in the rear area and the components arranged in the front area to one another, fairly long lines have to be laid for the fuel. For this reason, efforts are made to keep the number of lines between the rear area and the front area as small as possible. As can be seen from FIG. 12, in the preferred exemplary embodiment selected for the hydraulic connection of the components of the rear area with the components of the front area, the fuel connection 10 and the flushing line 60 are advantageously sufficient.

In order to facilitate a restart of the internal combustion engine 32 when the internal combustion engine 32 is switched off at a relatively high temperature, the following procedure is proposed: When the internal combustion engine 32 is switched off with the shut-off valve 30 still open, the first force occurs over a predetermined period of time, which may be temperature-dependent cloth pump 6 kept in operation. As a result, thermal energy that accumulates from the area of the second fuel pump 12 and from the area of the fuel connection 10 and the pressure accumulator 78 is dissipated via the flushing line 60 into the fuel reservoir 2 . This reduces the risk of unwanted gas bubbles forming in the fuel lines. In addition, it can be provided that, after flushing the fuel connection 10 , shortly before switching off the electrically driven fuel pump 6 , the shut-off valve 30 is switched to its closed switching position 30 b. As a result, the pressure in the fuel connection 10 and in the pressure damper 78 increases to the feed pressure determined by the pressure valve 7 , which is higher than the feed pressure determined by the pressure control valve 26 when the shut-off valve 30 is open. It is thereby achieved that there is an increased pressure in the pressure damper 78 when the internal combustion engine is switched off, which considerably facilitates the subsequent start of the internal combustion engine 32 even at high temperature.

The embodiments shown in FIGS. 1 to 8 are used in particular when the second fuel pump 12 has a plurality of pump pistons 12 p, usually three pump pistons 12 p. The guides are shown in FIGS. 9 to 12 illustrated in particular from used when the second fuel pump 12 has a single pump piston 12, p.

Claims (15)

1. Fuel supply system for supplying fuel for an internal combustion engine, with a fuel reservoir ( 2 ), a first fuel pump ( 6 ), a second fuel pump ( 12 ) and with at least one fuel valve ( 16 ), the first fuel pump ( 6 ), the fuel from the fuel tank ( 2 ) in a fuel connection ( 10 ) and the second fuel pump ( 12 ) promotes the fuel from the fuel connection ( 10 ) via a pressure line ( 14 , 42 , 44 ) to the fuel valve ( 16 ), via which the fuel at least indirectly into a combustion chamber of the internal combustion engine, with a fuel line ( 22 ) leading from the fuel connection ( 10 ) to the fuel reservoir ( 2 ) and with a pressure control valve ( 26 ) in the fuel line ( 22 ), characterized in that in the fuel line ( 22 ) hydraulically in series with the pressure control valve ( 26 ) a shut-off valve ( 30 ) and a fuel line ( 60 ) leading to the fuel tank ( 2 ) is provided at least partially through the second fuel pump ( 12 ) and through a hydraulic resistor ( 61 , 62 , 66 , 70 , 72 , 76 , 84 ). 2. Fuel supply system according to claim 1, characterized in that the shut-off valve ( 30 ) is controlled as a function of a temperature. 3. Fuel supply system according to claims 1 or 2, characterized in that the flushing line ( 60 ) through a pump housing ( 12 g) of the second fuel pump ( 12 ) is guided. 4. Fuel supply system according to one of the preceding claims, characterized in that the hydraulic resistance ( 61 , 62 , 66 , 70 , 72 , 76 , 84 ) is formed by a pressure-dependent opening valve ( 61 , 62 , 66 , 72 ). 5. Fuel supply system according to one of the preceding claims, characterized in that the hydraulic resistance ( 61 , 62 , 66 , 70 , 72 , 76 , 84 ) is formed by a valve ( 70 , 76 , 84 ) which is dependent on the fluid flow flowing through Has flow resistance. 6. Fuel supply system according to one of the preceding claims, characterized in that the flushing line ( 60 ) opens hydraulically between the shut-off valve ( 30 ) and the pressure control valve ( 26 ) in the fuel line ( 22 ). 7. Fuel supply system according to one of the preceding claims, characterized in that a pressure relief valve ( 7 ) is provided hydraulically parallel to the pressure control valve ( 26 ). 8. Fuel supply system according to one of the preceding claims, characterized in that one of the pressure line ( 14 , 42 , 44 ) via a control valve ( 50 , 50 ') in the fuel connection ( 10 ) leading circulation line ( 52 , 52 ') is provided and that the flushing line ( 60 ) branches off from the circulation line ( 52 , 52 '). 9. The fuel supply system according to claim 8, characterized in that the circulation line ( 52 , 52 ') leads via a resistance element ( 53 , 74 , 80 ) into the fuel connection ( 10 ). 10. Fuel supply system according to claim 8 or 9, characterized in that the circulation line ( 52 , 52 ') via a check valve ( 53 , 80 ) leads into the fuel connection ( 10 ). 11. Fuel supply system according to claim 10, characterized in that a throttle ( 74 ) is provided hydraulically parallel to the check valve ( 53 ). 12. Fuel supply system according to claim 3, characterized in that the flushing line (60) branches off at a highest point of the low-pressure side (12 n) of the second fuel pump (12) from the pump housing (12 g). 13. Fuel supply system according to claim 8, characterized in that the second fuel pump ( 12 ) has a compression space ( 12 k) and the circulation line ( 52 ') leads out of the compression space ( 12 k). 14. Fuel supply system according to one of the preceding claims, characterized in that one of the second fuel pump ( 12 ) in the fuel reservoir ( 2 ) leading leakage line ( 88 ) is provided. 15. Fuel supply system according to claim 14, characterized in that the leakage line ( 88 ) opens upstream of the shut-off valve ( 30 ) in the fuel line ( 22 ).